Research On Adaptive Sliding Mode Control Based On Disturbance Observer For Underactuated Surface Vessel Trajectory Tracking

In order to ensure the safe navigation of the ship,and to consider the comprehensive economic benefits of shipping,people have put forward a higher level of requirements for the motion control of the ship.The rapid development of the modern shipping industry has led to the deepening of the maritime traffic intensity at sea.Accurate ship track control,not only can reduce the number of helmsman operation,shorten the sailing distance,save fuel,and meet the needs of some special work ship.Conventional surface ships are mostly underactuated,so the control of the underactuated surface vessels has important practical value for the development of the shipping industry.The underactuated surface vessel is a class of special nonlinear system,which has the characteristics of large inertia,strong coupling,nonholonomic and uncertain model parameters.For the cumbersome nonlinear system,the main difficulty in studying ship tracking control is how to deal with its nonlinearity and uncertainty,the conventional control couldn't have the desired tracking effect.In order to meet the needs of normal shipping and promote the development of modern shipping industry,the introduction of new control strategies is imminent for the underactuated surface vessels.In this paper,the sliding mode control of the trajectory tracking is studied.The specific discussion is as follows:First,after reasonable simplification,the mathematical model of the underactuated surface vessels under the three degrees of freedom in the horizontal plane is established,and then carried out horizontal direct flight and horizontal plane simulation experiments to verify the direct flight performance and rotary performance of the model.It describe the correctness and validity of the model to provide the necessary conditions for the subsequent controller design.Secondly,the design of the tracking controller is divided into two parts using the traditional sliding mode control method.In the motion loop controller design,the realtime position tracking problem is transformed into the realtime speed tracking problem.And a new virtual reference speed is designed.And then use a robust sliding mode control method to design dynamic loop controller.The controller consists of longitudinal thrust sliding mode control law and rotary torque sliding mode control law.The Lyapunov stability condition and the sliding surface condition are used to determine the parameters of the sliding mode controller.The determination of the control method parameters is calculated under the condition that the parameter perturbation and the external disturbance are known.Thirdly,in order to solve the chattering problem of the sliding mode controller and to improve the accuracy of the system tracking,we convert the kinetic equation of the underactuated surface vessels to a typical MIMO system considering the influence of the parameter perturbation and the external environment disturbance in the ship model and design an adaptive sliding mode ship tracking controller based on disturbance observer.The perturbation of the model parameters is regarded as a kind of internal disturbance,and the nonlinear disturbance observer is used to estimate the time-varying interference,and the equal compensation is added to the controller,so as to achieve the purpose of suppressing the interference.For the chattering problem in the traditional sliding mode controller,the boundary layer theory is introduced,and the thickness of the boundary layer is adjusted in real time to achieve the purpose of weakening the buffeting and improving the control precision.Finally,the simulation results show that the designed controller can better estimate the composite interference,and the tracking accuracy is improved compared with the traditional sliding mode controller,and the controller design is reasonable and effective.